Field of the Invention
The present invention relates in general to the field of electronics, and more specifically to methods and systems of multiple power sources for a switching power converter controller.
Description of the Related Art
Many systems utilize integrated circuit controllers. Each controller generally operates from an alternating current (AC) or direct current (DC) power source. In some embodiments a higher voltage source, such as a 60 Hz/110 V line voltage in the United States of America or a 50 Hz/220 V line voltage in Europe, is available to supply power to the controller. However, the voltage requirements of the controller are generally significantly less than the available line voltage. Thus, for efficiency, the controller often receives power from an auxiliary power supply that supplies a voltage that more closely matches the maximum voltage requirements of the controller. However, the auxiliary power supply often generates power from the line voltage source and, thus, cannot begin delivering start-up power to the controller instantaneously. Accordingly, many controllers receive start-up power from the higher voltage source and fully or partially switch the auxiliary power source to deliver steady-state operating power.
FIG. 1 depicts an electronic system 100 that includes an IC controller 102 that controls delivery of power by switching power converter 104. Voltage source 106 supplies an alternating current (AC) input voltage VIN to a full bridge diode rectifier 108. The voltage source 106 is, for example, a public utility, and the AC voltage VIN is, for example, a 60 Hz/110 V line voltage in the United States of America or a 50 Hz/220 V line voltage in Europe. The full bridge rectifier 108 supplies a rectified AC voltage VX to the switching power converter 104. Capacitor 110 filters high frequency components from rectified voltage VX.
Voltage source 112 supplies an initial start-up current iSU and an operating voltage VDD. Voltage source 112 includes resistor 114 and capacitor 116. Resistor 114 is connected between node 118 at rectified voltage VX, and node 120 and supplies a current path for the initial start-up current iSU. The initial start-up current iSU charges capacitor 116, and capacitor 116 holds node 120 at a direct current (DC) operating voltage level VDD.
When node 120 reaches the operating voltage level VDD, controller 102 begins controlling switching power converter 104. Switching power converter 104 is a boost-type power converter that boosts the rectified voltage VX to generate a substantially DC link voltage VLINK across link capacitor 122. Link capacitor 122 supplies current to energize the primary coil 123 of transformer 125 when FET switch 127 conducts. To control the switching power converter 104, controller 102 generates switch control signal C0 to control the conduction state of a field effect transistor (FET) switch 124. When switch 124 conducts, the inductor current iL energizes inductor 126. Diode 129 prevents link capacitor 122 from discharging through switch 124. When switch 124 stops conducting, inductor 126 discharges, and inductor current iL replenishes the charge on link capacitor 122 to maintain the link voltage VLINK at a substantially constant value. Controller 102 also generates switch control signal C1 to control conductivity of switch 127, and, thus, control current flow into primary-side coil 123.
Transformer 125 includes two secondary-side coils. When the controller 102 begins controlling switching power converter 104 and switching power converter 104 begins generating the link voltage VLINK and energizing primary-side coil 123, secondary-side coil 128 supplies a load voltage VLD across capacitor 130 to load 132. Diode 133 prevents capacitor 130 from discharging through the secondary-side coil 128. Load 132 can be any type of load, such as a lighting system that includes any type of light source(s) such as one or more light emitting diodes (LEDs) or one or more fluorescent light sources, one or more motors, or one or more portable power sources.
Electronic system 100 includes an auxiliary power supply 133 that supplies power to controller 102 during steady-state operation. The auxiliary power supply 133 includes auxiliary coil 134, and auxiliary coil 134 represents the other secondary-side coil of transformer 125. Auxiliary coil 134 energizes when secondary-side coil 128 begins energizing. Auxiliary coil develops a voltage equal to the operating voltage VDD and supplies a post start-up, operating current iPSU_OP to controller 102. The auxiliary power supply 133 also includes diode 136 and Zener diode 138. Diode 136 prevents reverse current flow into auxiliary coil 134, and Zener diode 138 maintains the voltage at node 120 at the operating voltage VDD. In some embodiments of electronic systems 100, switching power converter 100 includes optional FET switch 140. Until the voltage across auxiliary coil 134 reaches the operating voltage VDD, controller 102 generates switch control signal C2 to cause switch 140 to conduct. When the voltage across auxiliary coil 134 reaches the operating voltage VDD, controller 102 generates switch control signal C2 to cause switch 140 to conduct and stop the start-up current iSU through resistor 114.
Electronic system 100 has several inefficiencies. For example, without switch 140, the start-up current iSU continues to flow through resistor 114 when the auxiliary coil 134 is energized and supplying current iPSU_OP. Current flow through resistor 114 generates power losses equal to the square of start-up current iSU times the resistance value of resistor 114. If electronic system 100 includes switch 140, controller 102 includes extra, well-known complexity to generate the control signal C2. Additionally, switch 140 is generally a high voltage FET, which is more expensive than a low voltage FET.